Our work is designed to explore the role of major histocompatibility antigens in the responses of T lymphocytes to foreign antigens. In particular, we would hope to better understand the relationship between T lymphocytes directly reactive to foreign MHC antigens and T lymphocytes reactive to non-MHC antigens associated with self MHC antigens. It is our thesis that such responses will involve the same T cells using the same receptor molecules. If this is so, then one would predict that T cells selected for reactivity to MHC antigens would also react to foreign, non-MHC antigens in the context of self MHC antigens, and our studies suggest that this is so. However, they are complicated by the complexity of T cell subsets. A more direct question is whether a single T cell gives rise to a clone of T cells with both potentialities, and we are currently preparing a number of such T cell lines to answer this question. Another aproach is to make antisera to the constant portion of the T cell receptor, and to determine if the T cell carries one or more than one type of receptor. Again, cloned T cell lines would give the most direct answer. Finally, we have prepared a large batch of antiserum that reacts specifically with T cell derived antigen-binding proteins and with suppressive T cell factors, and are using this to purify T cell derived poducts. The ability of these products to bind to antigen and to MHC antigens will be determined to find out if the T cell has one or two types of receptor on its surface.